The current ANSI/TIA-568-C.2 structured cabling standard defines the requirements for component and channel operation from Category 5e (CAT5E) to Category 6A (CAT6A), including requirements for RJ45 type plugs such as are commonly used in communication networks. Such plugs typically are connected to respective four-twisted-pair communication cables, and can mate with RJ45 jacks in a variety of network equipment such as patch panels, wall jacks, Ethernet switches, routers, servers, physical layer management systems, power-over-Ethernet equipment, security devices (including cameras and sensors), and door access equipment. RJ45 plugs can also mate with RJ45 jacks in workstation peripherals, such as telephones, fax machines, computers, printers, copiers, and other equipment. Plugs are components in corresponding channels, which channels can connect a user's computer to a router, for example, providing connection to the Internet, or other local area network (LAN) devices.
A typical structured cabling environment can include a commercial building having offices/work areas with computer workstations which are connected to a LAN, and to the Internet via patch panels, wall jacks, Ethernet switches, routers, servers, and/or physical layer management systems. A variety of cabling/cords such as patch cords, zone cords, backbone cabling, and horizontal cabling are used throughout the building to interconnect the aforementioned equipment. Cabinets, racks, cable management, overhead routing systems, and other such equipment can be used to organize the equipment and cabling into a manageable system.
As the complexity, data rate and frequency of operation increase for such communication networks, so increases the potential for undesirable interactions between the different channel components such as plugs, jacks and cable. As with any communication system, these communication networks have minimum signal-to-noise requirements to reliably transmit and receive information sent through the channel. A channel in such systems includes the four-twisted-pair (four transmission lines) transmission medium operating in full duplex communication mode. For 10 gigabit Ethernet (CAT6A), for example, each twisted pair (circuit) is operating at 2.5 gigabit/s to give the corresponding channel the full 10 gigabit capacity. One form of noise in such channels is crosstalk, which is a disturbance in a circuit (or a cable pair) signal, caused by a signal in an adjacent circuit (cable pair).
Crosstalk can be characterized as occurring at the near-end (NEXT) and the far-end (FEXT) of a transmission line between differential conductive path pairs within a channel (referred to as internal NEXT and internal FEXT) or can couple to differential conductive path pairs in a neighboring channel (referred to as alien NEXT and alien FEXT). Because of the differential signals which are typically used in such communication systems, so long as the same noise signal (common mode noise) is added to each conductive path in the conductive path pair, then the voltage difference between the conductive paths remains the same and such common mode crosstalk has no effect on the differential signal, for a given twisted pair.
As data transmission rates have steadily increased, crosstalk due to capacitive and inductive couplings, due at least in part to the distributed electrical parameters of the various circuit components, among the closely spaced parallel conductors within the plug and/or jack has become increasingly problematic. If the capacitive and inductive couplings between the four pairs of a channel are not equal, an imbalance exists, and the consequence of such imbalance is phenomenon called mode conversion. In mode conversion, common mode noise is converted to a differential signal, and the differential signal can be converted to a common mode signal. What may have been a relatively harmless common mode signal from a nearby channel, in the presence of circuit imbalance in the victim channel, is converted to differential signal in the victim channel thereby detrimentally reducing the signal to noise ratio of the victim channel. FIGS. 1A and 1B show a typical communication plug, with the plug body shown translucent to illustrate internal wires and contacts. FIG. 1A is an upper right-hand perspective view and FIG. 1B is an upper plan view. The plug 100 includes an RJ45 plug body 102 and a strain relief boot 114. Four differential wire pairs 108 (108a, 108b, 108c, and 108d) are disposed within the plug body.
During a typical installation, the pairs 108 are untwisted, aligned into the plug body 102, and crimped with a handheld tool so that the pairs 108 make contact with the insulation piercing contacts (IPCs) 109 at the nose of the plug. The IPCs provide the connection point when the plug 100 is inserted into an RJ45 jack. Although this design is per the ANSI/TIA-568-C.2 structured cabling standard, this design results in unbalanced capacitive and inductive coupling between neighboring conductors in the IPC area and along the untwisted parallel portion of the wires within the plug body 102. For interoperability and backwards compatibility, ANSI/TIA-568-C.2 requires that the plug have internal crosstalk within a de-embedded range, and that contacts 1 through 8 are arranged in order with contact 1 adjacent to contact 2, which is adjacent to contact 3, etc. This orientation of contacts results in an inherently unequal amount of coupling between the conductors of each pair. Capacitive and inductive coupling between neighboring circuits is highly dependent on proximity, i.e., the closer a victim circuit is to an aggressor circuit the higher the coupling, and consequently, the greater the coupled signal in the victim circuit. The capacitive and inductive coupling between conductor 3 of pair 3-6 and conductor 2 of pair 1-2 is much stronger than the capacitive and inductive coupling between conductor 3 of pair 3-6 and conductor 1 of pair 1-2 due to the closer proximity between conductor 2 of pair 1-2 and conductor 3 of pair 3-6. This poor balance leads to mode conversion, which causes a portion of a differential signal propagating through the plug on pair 1-2 to be converted to a common mode signal on pair 1-2. Due to the reciprocal nature of mode conversion, a portion of any common mode signal propagating though the plug on pair 1-2 will be converted to a differential signal on pair 1-2. The negative impact from poor balance and the associated mode conversion in the RJ45 plug 100 can be seen in many of the measurements made on a Category 6A channel, such as alien crosstalk parameters (e.g. power sum alien near-end crosstalk (PSANEXT) and power sum alien attenuation to crosstalk ratio, far-end (PSAACRF)) and balance parameters (e.g. transverse conversion loss (TCL) and transverse conversion transfer loss (TCTL)). The manufacturing inconsistencies of the manual untwisting process mentioned above can also lead to performance variability.
Poor balance in the plug 100 and the corresponding mode conversion may also lead to degraded electromagnetic interference/electromagnetic compatibility (EMI/EMC) performance for a Category 6A channel. The common mode signal that is created from a differential signal passing through an unbalanced plug 100 will radiate into the surrounding environment. Higher mode conversion corresponds to greater radiated energy. Conversely, when a channel is subjected to electromagnetic interference from outside sources such as walkie talkies, cellphones, etc., a common mode signal is induced in the channel. When that common mode signal passes through an unbalanced plug 100, a portion of that signal is converted to a differential signal, which will contribute to the total noise in the channel. Higher mode conversion results in proportionally higher differential noise.
Another shortcoming of the typical RJ45 plug 100 relates to the “super-pair” phenomenon. Industry standards require the plug contacts to have contacts 3 and 6 split around contacts 4 and 5. In the plug 100, wire pair 3-6 (reference numeral 108b) is also split around wire pair 4-5 (reference numeral 108c). This splitting of wire pair 3-6 results in conductor 3 coupling more strongly than conductor 6 to pair 1-2 (reference numeral 108a) and conductor 6 coupling more strongly than conductor 3 to pair 7-8 (reference numeral 108d). Because the signal on conductor 3 is at the opposite polarity of the signal on conductor 6, pair 1-2 will be at the opposite polarity of pair 7-8. Depending on the design of the connecting hardware and cabling, pair 1-2 and pair 7-8 may act as a differential “super-pair” and propagate the crosstalk from pair 3-6 through the channel. The “super-pair” signal can degrade the PSANEXT and PSAACRF performance of a Category 6A channel.
What is needed in the art is a communication plug which has balanced coupling between pairs resulting in balanced crosstalk between the four pairs, which can provide improved PSANEXT, PSAACRF, TCL, and/or TCTL performance as well as enhanced EMI/EMC performance caused by lowered electromagnetic radiation and higher tolerance of electromagnetic field levels from interfering sources.